In an inkjet printer, better print quality may be achieved by activating each resistive heater element with the same current. However, during the operation of the printer, the current delivered to a heater element in a typical chip is dependent on the electrical effects of varying circuit parasitic resistances. Such parasitic resistances may result from different material thicknesses, compositions and dimensional variations caused by etching and different logic switch resistances for each heater element. The different parasitic resistances may change the voltage and dm current supplied to the beater element and may thereby affect prim quality. One example of this occurs when multiple heater elements attached to the same power line are fired or actuated simultaneously, (i.e. multiple heater elements are “on” during a particular time interval). A parasitic resistance is associated with the power lines leading to each of the heater elements. When multiple elements are fired at the same time, the current passing through the power line prior to reaching the elements increases proportionally to the number of heater elements fired. The increasing current, causes an increased voltage drop across the power line parasitic resistance and thus reduces the current supplied to each element. Additionally, when multiple heater elements are fired at the same time, the parasitic resistance associated with each heater element increases proportionally to the element's physical distance away from the power line. Therefore, the current through each element decreases in proportion to the element's distance from the power line. Thus, heat produced by each element may be inconsistent depending upon the number of elements actuated thereby affecting the print quality.
Better print quality may also be achieved in an inkjet printer by maintaining a constant current through each resistive heater element for the duration of the neater actuation (i.e., the fire pulse). During actuation of the resistive heater element, the heater material temperature coefficient may cause a change in the heater element resistance over the duration of the fire pulse (i.e., as the heater element heats up). The change in the resistance may cause the heat provided by each element to change during the fire pulse. Such a change in heat may affect the consistency of the ejection of fluid onto the media during the fire pulse.
Accordingly, there is a need to improve the consistency of the current (i.e. fire pulse) provided to each actuated heater element regardless of the number of elements actuated or the heater material temperature coefficient.